1. Field of the Invention
The present invention relates to a display technique that provides, for example, forgery-preventing effect, decorative effect and/or aesthetic effect.
2. Description of the Related Art
For forgery prevention, latent images are used in some cases. A latent image can be produced utilizing line screen moiré or intaglio printing, for example.
A latent image utilizing line screen moiré can be obtained by superposing an image to be produced as a latent image on a multiple of lines arranged at a high density. The image is difficult to discriminate due to the multiple lines when observed by the unaided eye, and is made easy to discriminate by hiding the lines.
A latent image utilizing intaglio printing can be obtained by forming a recessed pattern and/or a protrusion pattern on an ink layer. The image produced by the recessed pattern and/or the protrusion pattern is difficult to discriminate when observed from the front, and is visualized when observed obliquely.
The forgery-preventing technique utilizing the line screen moiré or the intaglio printing is comparatively easy in discriminating a genuine one from a counterfeit. However, the images produced by such methods are not the ones that are impossible to discriminate when observed by the unaided eye. Thus, the presence of the latent images is prone to be noticed.
A latent image can also be produced using special ink such as fluorescent ink or infrared radiation-absorbing ink. Fluorescent ink is the one that emits light when exposed to ultraviolet radiation, and a latent image produced using this is visualized by ultraviolet irradiation. Infrared radiation-absorbing ink is the one that is high in absorptance for infrared radiation, and a latent image produced using this is visualized when observed using an infrared camera, for example.
The presence of a latent image produced using the special ink is less prone to be noticed. However, in order to visualize it, an ultraviolet lamp or an infrared camera is necessary.
A latent image can also be produced using a liquid crystal material. For example, a patterned thin layer made of a solidified liquid crystal material such as liquid crystal polymer is formed on a substrate having light-reflecting property. The mesogens of the liquid crystal molecules are aligned almost in a single direction by subjecting the surface underlying the patterned thin film to an alignment process such as rubbing process or photo-alignment process.
When observed by the unaided eye, the patterned thin film is seen in the same manner as an optically isotropic layer. Thus, a latent image can be produced using the patterned thin film. In addition, since the patterned thin film functions as a retardation layer, when observed through a polarizer, it causes a change in brightness according to the angle that the slow axis forms with the transmission axis of the polarizer. That is, the latent image that the patterned thin film produces is visualized when observed through a polarizer.
The presence of a latent image produced using a liquid crystal material is less prone to be noticed. In addition, this latent image can be visualized with a polarizer such as polarizing film, thus a bulky apparatus is unnecessary. For these reasons, the forgery-preventing technique utilizing a liquid crystal material attracts keen interest.
For example, JP-A 2001-63300 (KOKAI) describes stacking an OVD (optically variable device) layer and a latent image formation layer one on the other. The latent image formation layer is, for example, made of a polymer liquid crystal material. The OVD layer is, for example, a hologram.
When observing such a layered structure by the unaided eye, the visual effect of the hologram, that is, iridescence and a color shift in accordance with the observation angle can be perceived. On the other hand, the latent image that the latent image formation layer produces is visualized when observed via a polarizer. Thus, the combined use of a liquid crystal material and a hologram makes it possible to produce an image that changes variously. Therefore, it is possible to achieve a greater forgery-preventing effect as compared with the case where only the liquid crystal material is used.
However, the technological advances are significant. Thus, a further advancement of the forgery-preventing technique is desired.